The present invention relates to navigation satellite receivers, and more particularly to methods and systems for off-loading the computational workload of a network client to a network server to compute a navigation fix.
The global positioning system (GPS) is a satellite-based radio-navigation system built and operated by the United States Department of Defense at a cost of over $13 billion. Twenty-four satellites circle the earth at an altitude of 20,200 km, and are spaced in orbit such that at any time a minimum of six satellites is in view to any user. Each satellite transmits an accurate time and position signal. A typical GPS receiver measures the time delay for the signal to reach it, and the apparent receiver-satellite distance can then be calculated. Measurements from at least four satellites allow a GPS receiver to calculate its position, velocity, altitude, and time.
A GPS receiver that has just been turned on does not yet know where it is, how much its crystal oscillator is in error, nor what time it is. All these are needed to find and lock onto the satellite transmissions, and so a search must be made of all the possibilities. Each GPS satellite vehicle (SV) transmits navigation (NAV) data that includes ephemeris, clock and almanac information. Such information allows a GPS receiver to compute its position, velocity, and time.
GPS receivers can be interconnected by a computer network to help one another with initialization and on-going navigation solutions.
The current state of development in electronics technology is now allowing excess processor and memory resources in consumer devices to be used in GPS navigation applications. For example, cellular telephones can benefit by being associated with a GPS receiver. But the computational workload and memory demands of a GPS receiver to find a navigation fix can be intense. At a minimum, a GPS receiver needs to collect pseudorange measurements from the GPS satellite vehicles (SV""s) it can see. Such observables can then be shipped off elsewhere to compute the navigation solution.
For example, the National Geodetic Survey (NGS) operates the On-line Positioning User Service (OPUS) provides GPS users with access to the National Spatial Reference System (NSRS). OPUS allows users to submit their GPS data files in RINEX format to NGS. The data is processed to find a navigation solution using NGS computers and software. Each RINEX file submitted is processed with respect to three CORS sites. The sites selected may not be the nearest site. They are selected by distance, number of observations, site stability, etc. The position corresponding to the input data is reported back via email. For example, such reports can be formatted in ITRF, NAD83, UTM, or State Plane Coordinates (SPC) northing and easting. OPUS is automatic and requires as input: the email address where the results are to be sent, the RINEX file to process, the antenna type used to collect such RINEX file, the height of the antenna reference point (ARP) above the monument or mark, and the state plane coordinate code for SPC northing and easting. Once this information is completed in a browser window, the user clicks an upload button to send the data to NGS. The results are emailed back a few minutes. The RINEX files can be uploaded one at a time.
It is therefore an object of the present invention to provide a GPS receiver that connects to a computer network as a client and that off-loads computational loads and memory demands onto a network server.
It is another object of the present invention to provide a method and system for off-loading GPS receivers that share resources with other consumer devices.
Briefly, a thin-client navigation-satellite receiver embodiment of the present invention collects GPS pseudorange measurements and communicates them from many independent clients on a computer network to a server. The server computes the respective navigation solutions and sends the results back to each client. A client manager at the server includes a client-request handler that interfaces with the network and collects the discrete requests from each of the clients. An assembler builds complete data sets from the data gathered by the client-request handler and spins each ready-to-go job to a bank of navigation servers. A session manager coordinates the inputs-and-results communication on the network and sends its outputs to a client responder.
An advantage of the present invention is that a system and method are provided for thin-client navigation satellite receivers.
Another advantage of the present invention is that a system and method are provided for making simple and inexpensive navigation satellite receivers.